EAS systems of the type described above, are, for example, disclosed and claimed in U.S. Pat. No. 3,665,449 (Elder and Wright). As set forth at Col. 5, lines 10 to 39 therein, a dual status marker of the type described above may be desensitized, i.e., the high-coercive force section thereof magnetized, by placing the marker in the field of a large permanent magnet of sufficient intensity, and gradually removing the field, such as by withdrawing the marker therefrom. As also there disclosed, such a magnetization operation may be effected by imposing on the marker a unipolar pulsed field of gradually decreasing intensity. That patent also suggests that desensitization may be effected by exposing the marker to fields of alternating polarity provided by an array of permanent magnets.
While such techniques may be useful in many areas and with the markers affixed to a wide variety of articles, the magnetic fields associated therewith have been found to unacceptably interfere with magnetic states associated with certain articles. For example, the compact size and popularity of prerecorded magnetic audio and video cassettes make such articles frequent targets for shoplifters, and hence likely articles with which anti-theft markers would be used. At the same time however, such affixed markers would be desirably desensitized upon purchase, and it has been found that prior art desensitizer apparatus such as described above may unacceptably affect signals prerecorded on magnetic tapes within the cassettes.